Radio frequency (RF) transceivers and receivers can be found in numerous applications, particularly in the field of wireless communications and radar sensors. In the automotive sector, there is an increasing demand for radar sensors used in so-called “adaptive cruise control” (ACC) or “radar cruise control” (RCC) systems. Such systems may be used, for example, to automatically adjust the speed of an automobile so as to maintain a safe distance from other automobiles or other objects ahead.
Modern radar systems make use of highly integrated RF circuits, which may incorporate all core functions of an RF font-end of a radar transceiver in one single chip package (single chip transceiver). Such RF front-ends may include, inter alia, a voltage controlled oscillator (VCO), amplifiers such as power amplifiers, low noise amplifiers (LNAs), mixers, filters. One or more analog-to-digital converters (ADC) may also be included to provide a digital output. Furthermore, the chip or the chip package may include one or more antennas. Radio frequency chips such as the semiconductor chips including the RF front-end of a radar sensor are also referred to as monolithic microwave integrated circuits (MMICs).
Radar applications used in automobiles are subject to various standards concerning road traffic safety, for example the functional safety standard ISO 26262 titled “Road vehicles—Functional safety”. To ensure the functional safety of a radar sensor, it is important to know whether the current state of the radar sensor allows a reliable distance and speed measurement. However, also in applications different from radar, reliability may be an issue.
In radar systems the overall noise floor limits the sensitivity, with which radar targets can be detected. In this regard it is noted that the phase noise properties of the on-chip oscillators may have a significant impact on the overall noise floor and thus on the sensitivity and accuracy of the distance and velocity measurement. To ensure that the on-chip RF oscillator operates within the desired specifications, the RF chips (MMICs), which include the RF oscillators, may be subject to various automatic tests including tests characterizing the noise properties of the on-chip RF oscillator. For an economic production the duration of these automatic tests and the number of chips that can be tested in parallel are important parameters.